This invention relates to micro-electromechanical systems (xe2x80x9cMEMSxe2x80x9d) and, more particularly, to micro-miniaturization of electrical switches and arming and firing devices having application in missiles, rockets, and like apparatus.
In order to prevent a rocket motor, warhead, explosive separation device or energetic material, collectively sometimes referred to as target devices, from being unintentionally operated during flight or in any circumstance that could produce an extreme hazard to personnel or facilities, an xe2x80x9carm firexe2x80x9d device is customarily incorporated in the firing control circuit for the foregoing devices as a safety measure. The arm fire device electrically and mechanically interrupts the xe2x80x9cignition trainxe2x80x9d to the target device so as to prevent accidental operation. The arm fire device includes a mechanism that permits the target device to be armed, ready to fire, only while electrical power is being applied to the target device. When that electrical power is removed, signifying the target device is disarmed, the mechanism of the arm fire device returns to a safe position, interrupting the path of the ignition train.
Another known device of similar purpose, is called the xe2x80x9csafe and armxe2x80x9d device, and is a variation of the arm fire device. The mechanism of the safe and arm device enables the target device, such as the rocket motor, warhead and the like, earlier mentioned, to remain armed, even after electrical power is removed. The device may be returned to a xe2x80x9csafexe2x80x9d position only by applying (or reapplying) electrical power. The safe and arm device is commonly used to initiate a system destruct in the event of a test failure, for launch vehicle separation and for rocket motor stage separation during flight. Typically, the safe and arm device uses a pyrotechnic output which may be either a subsonic pressure wave or which may be a flame front and supersonic shock wave or detonation to transfer energy to another pyrotechnic device (and serves as the trigger of the latter device).
The foregoing safety devices have been proven in service. Constructed using existing technology, those safety devices are typically of the size of a person""s fist, and possess a noticeable weight of several pounds. If the weight and volume of those devices can be reduced, the payload and propulsion systems can be increased in weight and/or volume to increase the range and capability of a weapon system. Given the goal of reducing weight and volume, the arm fire device and the safe and arm device are candidates for significant miniaturization in the system. As an advantage the present invention addresses the function of arm fire devices and safe and arm devices, and accomplishes the functions of the foregoing devices in an electromechanical apparatus that is significantly smaller in size and weight than the presently existing counterparts.
Micro-electromechanical systems (xe2x80x9cMEMSxe2x80x9d) have become known to a degree. The MEMS devices reported in the literature represents an achievement milestone in miniaturization and integration of electromechanical machines and devices. That technology provides, as example, a toothed gear that is smaller in size than a speck of dust, invisible to the eye. MEMS devices are sometimes fabricated by employing the photo-lithograph mask and etch techniques familiar to those in the semiconductor fabrication technology to form micro-miniature parts of silicon, which are annealed to strengthen the part. In copending application Ser. No. 08/912,709, a micro-miniature pyrotechnic gas generator, called a micro-thruster is described that is capable of issuing a microburst of gas in which the expelled gas is applied to produce thrust for a micro-satellite or other small craft.
Accordingly, a principal object of the invention is to micro-miniaturize arm fire and safe and arm devices.
Another object of the invention is to provide electrical single operation switch designs for fabrication using MEMS fabrication techniques.
An ancillary object of the invention is to produce micro-miniature single operate electrical switches.
Miniaturized light-weight arm fire and safe and arm devices are made possible by incorporating the advantages of micro-electromechanical system (xe2x80x9cMEMSxe2x80x9d) technology in the devices. In accordance with the invention, arm fire and safe and arm devices include an electrically operated pyrotechnic initiator or, as variously termed, MEMS ignition device to generate a pyrotechnic output upon command and an electro-mechanically movable pyrotechnic barrier that blocks propagation of the shock wave and expanding gases of the pyrotechnic output if the device is not intended to be fired. The pyrotechnic output is transferred from the device for use in igniting an explosive train, either directly or indirectly, the latter, as example, by operating an electrical switch. To prevent output through unintended operation of the MEMS ignition device the pyrotechnic barrier is normally positioned to block the output; and the barrier is moved out of the way when output is desired. In the arm fire device, the barrier automatically prevents an output when electrical power is removed from the unit. In the safe and arm device, the barrier, once moved out of the way, remains out of the way, even when electrical power is removed.
As an additional feature, the switch operator of a micro-miniature electrical switch receives the pyrotechnic output and is moved in position by the pyrotechnic output to close a pair of normally open electrical contacts. The contacts may be included in an electrically operated explosive train.
An ancillary invention in a miniature single operation electrical switch includes an electrically operated MEMS gas generator, a movable switch operator and a pair of electrical contacts. On applying a current pulse, a microburst of hot gas is generated that forces the switch operator to shift in position to change the condition of a DC current path through the electrical contacts.
The foregoing and additional objects and advantages of the invention together with the structure characteristic thereof, which was only briefly summarized in the foregoing passages, will become more apparent to those skilled in the art upon reading the detailed description of a preferred embodiment of the invention, which follows in this specification, taken together with the illustrations thereof presented in the accompanying drawings.